DOCSLIB.ORG

U-Pb Zircon Dating of Basement Inliers Within the 2 Moine Supergroup, Scottish Caledonides: Implications of Archaean 3 Protolith Ages 4 5 C.R.L

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
U-Pb Zircon Dating of Basement Inliers Within the 2 Moine Supergroup, Scottish Caledonides: Implications of Archaean 3 Protolith Ages 4 5 C.R.L 11/12/06 Inliers -revised 1 1 U-Pb zircon dating of basement inliers within the 2 Moine Supergroup, Scottish Caledonides: implications of Archaean 3 protolith ages 4 5 C.R.L. Friend 1, R.A. Strachan2, P.D. Kinny 3 6 7 8 1. 45, Stanway Rd., Risinghurst, Headington, Oxford OX3 8HU, UK 9 10 2. School of Earth & Environmental Sciences, University of Portsmouth, Burnaby Road, 11 Portsmouth PO1 3QL, UK 12 13 3. The Institute for Geoscience Research, Department of Applied Geology, Curtin University of 14 Technology, GPO Box U1987, Perth, WA 6845, Australia 15 16 17 18 Abstract: Basement gneiss inliers within the Scottish Caledonides have been 19 conventionally correlated with the Archaean Lewisian Gneiss Complex of the Caledonian 20 foreland. Alternatively, the inliers could represent allochthonous terranes accreted to 21 Laurentia before or during the Caledonian orogeny. SIMS U-Pb zircon dating indicates 22 that the Ribigill, Borgie, Farr and Western Glenelg basement inliers are characterized by 23 late Archaean protolith ages, and a period of isotopic disturbance in the late 24 Palaeoproterozoic. The data are broadly consistent with correlation between the inliers and 25 components of the Lewisian Gneiss Complex of the Caledonian foreland. The c. 2900 Ma 26 protolith ages support correlation of the Borgie and Farr inliers with the Assynt terrane, 27 and a younger, c. 2800 Ma age for the Ribigill inlier supports correlation with the 28 Rhiconich terrane. None of the studied inliers shows a complete match of protolith and 29 early metamorphic histories with any of the Lewisian basement terranes, but differences 30 between the inliers and the foreland are no greater than those recorded within the foreland 31 basement terranes themselves. Therefore, it remains probable that the dated inlier gneisses 32 formed a distal part of the Laurentian margin prior to final telescoping during the 33 Caledonian orogeny. [end of abstract] 34 35 The complexity of many collisional orogens results, at least in part, from the tectonic 36 assembly of disparate crustal blocks to result in collages of fault-bounded ‘suspect’ or 37 ‘allochthonous’ terranes that have become detached from the cratons from whence they 38 originated. One of the main challenges in such a setting involves the identification of 11/12/06 Inliers -revised 2 39 individual terranes and their possible cratonic sources, and hence an evaluation of the 40 likely displacements along the terrane-bounding faults. In some Phanerozoic orogens the 41 history of terrane accretion and estimates of likely displacements along terrane boundaries 42 can be resolved by palaeomagnetic and palaeontological methods. In older orogens, 43 particularly those characterized by unfossiliferous strata and/or medium to high-grade 44 metamorphic rocks, identification of terranes and the nature of their original relationship to 45 cratonic foreland rocks is considerably more difficult. Correlation of a terrane with a 46 cratonic foreland requires the identification of common geological features, many of which 47 may have been eroded in older orogens. In such cases, a potential method of analysis 48 involves the characterization of basement rocks in a given terrane, and comparison with 49 the basement rocks of adjacent cratonic forelands. This method may encounter problems 50 as a result of the extensive reworking and resetting of isotopic systems that are common in 51 basement complexes and in orogens, but may be the only tool available for terrane 52 analysis. Despite the potential difficulties, this is the approach adopted in this paper where 53 U-Pb geochronology has been used to characterize basement inliers within the Lower 54 Palaeozoic Caledonide orogen of northwest Scotland, and to assess potential linkages with 55 the Laurentian foreland west of the Moine Thrust Zone (Fig 1). 56 Within the Caledonide orogen in northwest Scotland (Fig. 1), there are numerous 57 inliers of highly deformed gneissic rocks that differ markedly in their lithological 58 characteristics and structural and metamorphic histories from the adjacent 59 metasedimentary rocks of the Neoproterozoic Moine Supergroup (e.g. Flett 1905; Peach et 60 al. 1910). These inliers have the appearance of crystalline basement now variably 61 overprinted with younger structures, many of which have been interpreted as Caledonian 62 (Ordovician-Silurian) in age (e.g. Rathbone & Harris 1979; Strachan & Holdsworth 1988; 63 Holdsworth 1989). A central problem within the Scottish Caledonides concerns the extent 64 to which the basement inliers and the Moine Supergroup are allochthonous with respect to 65 the Laurentian foreland west of the Moine Thrust Zone (Fig. 1). The foreland comprises 66 the Archaean – Palaeoproterozoic Lewisian Gneiss Complex (e.g. Friend & Kinny 2001; 67 Park et al. 2002; Kinny et al. 2005) that is overlain unconformably by the late 68 Mesoproterozoic to Neoproterozoic Torridonian sedimentary rocks (e.g. Stewart 2002). 69 Mainly on lithological grounds, the basement inliers have been correlated previously with 70 the Lewisian Gneiss Complex (e.g. Johnstone 1975; Rathbone & Harris 1979), and the 71 Moine Supergroup sediments with the Torridonian (e.g. Cheeney & Matthews 1965). If 11/12/06 Inliers -revised 3 72 such correlations are correct, they imply that the basement inliers and the Moine rocks 73 evolved as part of Laurentia during the Precambrian. An alternative view is that these rock 74 units form part of an allochthonous terrane that was accreted to the Laurentian margin 75 either prior to or during the Caledonian orogeny (e.g. Bluck et al. 1997). 76 Attempts to evaluate Moine-Torridonian linkages have noted that the two 77 sequences have slightly different detrital zircon suites (Rainbird et al. 2001; Friend et al. 78 2003; see however, Krabbendam et al. 2008), and moreover the Moine rocks were affected 79 by mid-Neoproterozoic (Knoydartian) orogenic events that are apparently absent on the 80 foreland (e.g. Rogers et al. 1998; Vance et al. 1998; Tanner & Evans 2003). Nevertheless, 81 neither of these differences necessarily precludes a Laurentian origin for the Moine rocks 82 (Cawood et al. 2004). As an alternative method of evaluating potential linkages across the 83 Moine Thrust Zone we provide in this paper new isotopic age data for four basement 84 inliers within the Moine Supergroup. We assess the resultant implications for possible 85 linkages with the Lewisian Gneiss Complex of the Laurentian foreland and regional 86 tectonic models for this part of the Caledonides. 87 88 Regional setting of basement inliers within the Caledonides of NW Scotland 89 90 Lithologies and structural setting 91 92 Inliers of basement rocks occur widely within the Moine Supergroup, mainly in the Moine 93 and Sgurr Beag nappes, and largely in contact with metasediments assigned to the Morar 94 and Glenfinnan groups. There are three main concentrations of inliers: those in northern 95 Sutherland below the Naver Thrust; those in the Scardroy-Fannich area; and those 96 immediately above the Moine Thrust in the Attadale – Glenelg – south Skye area (Fig. 1). 97 Numerous smaller inliers are also present within other parts of the Moine and Sgurr Beag 98 nappes. The inliers lie consistently at the lowest structural levels of local stratigraphical 99 successions once the effects of thrusting and/or folding are removed. Some inliers 100 apparently lie in the cores of isoclinal folds e.g. Morar (Kennedy 1955; Powell 1966) and 101 Naver (Strachan & Holdsworth 1988), whereas others are allochthonous slices underlain 102 by Caledonian thrusts such as the Sgurr Beag Thrust (e.g. Tanner et al. 1970; Rathbone & 103 Harris 1979) and the Ben Hope Thrust (Holdsworth 1989). 11/12/06 Inliers -revised 4 104 Most inliers are dominated by tonalitic to dioritic hornblende-rich gneisses that are 105 commonly highly deformed and variably banded with polyphase pegmatitic material. Thin 106 strips of pelitic metasediment and marble have been recognized in some inliers (e.g. Loch 107 Shin, Eastern Glenelg) and appear to represent an integral part of the basement 108 assemblage. Throughout all of the inliers, the dominant metamorphic assemblages now 109 present are amphibolite facies or lower, as the gneisses have been extensively reworked 110 and retrogressed during Knoydartian (820-730 Ma) and Caledonian (470-420 Ma) 111 orogenic events. Some inliers locally preserve evidence of high-grade, pre-Caledonian 112 metamorphic assemblages. These include the Western Glenelg inlier where relict granulite 113 facies mineralogies are preserved (e.g. Barber & May 1975; Sanders 1979) and the Eastern 114 Glenelg inlier where eclogite facies rocks are present (e.g. Teall 1891; Alderman 1936; 115 Mercy & O’Hara, 1969; Sanders 1979; Sanders et al. 1984). Early high-grade assemblages 116 have also been reported from the Borgie inlier where garnet and clinopyroxene-bearing 117 mafic gneisses were retrogressed into amphibole-plagioclase assemblages during the 118 Caledonian orogeny (Moorhouse 1976; Holdsworth et al. 2001). 119 120 Affinities of the basement inliers and relationships with the Moine Supergroup 121 122 When the basement inliers within the Moine Supergroup were first mapped they were 123 interpreted to be sub-Moine, Lewisian rocks because of their lithological similarity to the 124 Lewisian gneisses of the Caledonian foreland (e.g. Flett 1905; Peach et al. 1907, 1910, 125 1913). This correlation was challenged by Sutton & Watson (1953, 1954), who 126 interpreted the gneissic rocks of central Ross-shire as integral parts of the Moine 127 succession. However, subsequent research in the Glenelg area showed this to be incorrect 128 (Ramsay 1958) and correlation with the Lewisian of the foreland was reinstated and 129 continued in later studies of the Moine nappes (e.g. Sutton & Watson 1962; Barber & May 130 1975; Rathbone & Harris 1979; Strachan & Holdsworth 1988; Holdsworth 1989; 131 Temperley & Windley 1997). It has been tacitly assumed on the basis of broad lithological 132 similarities that all of the inliers belong to essentially the same portion of the Lewisian 133 (e.g.
Load more

Recommended publications
  • Sedimentology of the Early Neoproterozoic Morar Group in Northern Scotland: Implications for Basin Models and Tectonic Setting H
    Sedimentology of the early Neoproterozoic Morar Group in northern Scotland: implications for basin models and tectonic setting H. C. Bonsor1*, R. A. Strachan2, A. R. Prave3 and M. Krabbendam1 1 British Geological Survey, Murchison House, West Mains Road, Edinburgh, EH9 3LA, UK * corresponding author: (H. C. Bonsor) email: [email protected] 2 School of Earth and Environmental Sciences, University of Portsmouth, Portsmouth, PO1 3QL, UK 3 Department of Earth Sciences, University of Andrews, St Andrews, KY16 9AL, UK Abstract The metasedimentary rocks of the Morar Group in northern Scotland form part of the early Neoproterozoic Moine Supergroup. The upper part of the Group is c. 2-3 km thick and contains two large km-scale facies successions: a coarsening-upwards marine-to-fluvial regression overlain by a fining-upwards fluvial-to-marine transgression. Fluvial facies make up less than a third of the total thickness; shallow-marine lithofacies comprise the remainder. Combining these new findings with previously published data indicates that the Morar Group represents, overall, a transgressive stratigraphic succession c. 6-9km thick, in which there is both an upward and eastward predominance of shallow-marine deposits, and a concomitant loss of fluvial facies. Smaller-scale (100s of m thick) transgressive-regressive cycles are superimposed on this transgressive trend. Collectively, the characteristics of the succession are consistent with deposition in a foreland basin located adjacent to the Grenville orogen, and possibly linked to the peri-Rodinian ocean. Subsidence and progressive deepening of the Morar basin may have, at least in part, been driven by loading of Grenville-orogeny- emplaced thrust sheets, and aided by sediment loading.
    [Show full text]
  • Structural, Petrological, and Tectonic Constraints on the Loch Borralan and Loch Ailsh Alkaline Intrusions, Moine Thrust Zone, GEOSPHERE, V
    Research Paper GEOSPHERE Structural, petrological, and tectonic constraints on the Loch Borralan and Loch Ailsh alkaline intrusions, Moine thrust zone, GEOSPHERE, v. 17, no. 4 northwestern Scotland https://doi.org/10.1130/GES02330.1 Robert Fox and Michael P. Searle 24 figures Department of Earth Sciences, Oxford University, South Parks Road, Oxford OX1 3AN, UK CORRESPONDENCE: [email protected] ABSTRACT during ductile shearing. The minerals pseudomor- Grit Members of the An t-Sron Formation) and the phing leucites show signs of ductile deformation Ordovician Durness Group dolomites and lime- CITATION: Fox, R., and Searle, M.P., 2021, Structural, petrological, and tectonic constraints on the Loch Bor- During the Caledonian orogeny, the Moine indicating that high-temperature (~500 °C) defor- stones (Woodcock and Strachan, 2000; Strachan ralan and Loch Ailsh alkaline intrusions, Moine thrust thrust zone in northwestern Scotland (UK) mation acted upon pseudomorphed leucite crystals et al., 2010; British Geological Survey, 2007). zone, northwestern Scotland: Geosphere, v. 17, no. 4, emplaced Neoproterozoic Moine Supergroup rocks, that had previously undergone subsolidus break- The hinterland of the Caledonian orogenic p. 1126– 1150, https:// doi.org /10.1130 /GES02330.1. meta morphosed during the Ordovician (Grampian) down. New detailed field mapping and structural wedge comprises schists of the Moine Super- and Silurian (Scandian) orogenic periods, westward and petrological observations are used to constrain group with structural inliers of Lewisian basement Science Editor: Andrea Hampel Associate Editor: Robert S. Hildebrand over the Laurentian passive margin in the north- the geological evolution of both the Loch Ailsh gneisses and intrusive Caledonian granites (Geikie, ern highlands of Scotland.
    [Show full text]
  • Morar Group Correlation
    Correlation of Torridon and Morar groups 1 2 A fluvial origin for the Neoproterozoic Morar Group, NW Scotland; implications 3 for Torridon - Morar group correlation and the Grenville Orogen Foreland Basin 4 5 Maarten Krabbendam (1), Tony Prave (2), David Cheer (2, 3), 6 (1) British Geological Survey, Murchison House, West Mains Road, Edinburgh EH9 7 3 LA, UK. Email: [email protected] Corresponding author. 8 (2) School of Geography & Geoscience, Irvine Building, University of St Andrews, 9 St Andrews KY16 9AL, UK 10 (3) Present address: Scotland TranServ, Broxden Business Park, Perth, PH1 1RA 11 12 Running title: Correlation of Torridon and Morar groups 13 14 Abstract 15 Precambrian sedimentary successions are difficult to date and correlate. In the 16 Scottish Highlands, potential correlations between the thick, undeformed siliciclastic 17 ‘Torridonian’ successions in the foreland of the Caledonian Orogen and the highly 18 deformed and metamorphosed siliciclastic Moine succession within the Caledonian 19 Orogen have long intrigued geologists. New and detailed mapping of the 20 Neoproterozoic A ‘Mhoine Formation (Morar Group, lowest Moine Supergroup) in 21 Sutherland has discovered low strain zones exhibiting well-preserved sedimentary 22 features. The formation comprises 3-5 kilometres of coarse, thick-bedded psammite 23 with abundant nested trough and planar cross-bedding bedforms, defining metre-scale 24 channels. Palaeocurrent directions are broadly unimodal to the NNE-ENE. We 25 interpret the A ‘Mhoine Formation as high-energy, braided fluvial deposits. The A 26 ‘Mhoine Formation and the unmetamorphosed, Neoproterozoic Applecross-Aultbea 27 formations (Torridon Group), are similar in terms of lithology, stratigraphical 28 thickness, sedimentology, geochemistry, detrital zircon ages and stratigraphical 29 position on Archaean basement.
    [Show full text]
  • Geological Notes and Location Descriptions for Field Excursions
    Inverness: 30 April - 7 May Inverness: 30 Geological notes and location descriptions for field excursions Deformation mechanisms, Rheology and Tectonics 2017 Deformation mechanisms, Rheology and Tectonics 1 Geological notes* The crustal evolution and geology of NW Scotland can be considered with reference to the Palaeozoic Caledonian orogeny. This major episode of crustal reworking was associated with the formation of a North Atlantic Craton – suturing the Proterozoic and older crustal blocks of Laurentian and Baltica (together with Avalonia, further south). NW Scotland contains part of the western margin of this orogen (or at least its more intense parts), a tectonic feature termed the Moine Thrust Belt. The foreland to the thrust belt preserves much older geology, exhumed from up to 35-40km depth, that give insight to processes that form, rework and reassemble the continental crust. The Caledonian rocks allow us to follow a transect from exhumed middle crustal sections within the orogen out into the foreland. Collectively these outcrops provide arrays of analogues for crustal geology and deformation structures, and we can use these to promote discussion of their geophysical characteristics when targeted in situ. However, the Caledonian crust, together with its foreland, has seen later deformation associated with the formation of sedimentary basins, chiefly in the immediate offshore. We can also access basin faults and examine not only their individual characteristics but also debate how they may have been influenced by pre-existing structures. Pre-Caledonian geology The Lewisian. The Lewisian forms the oldest basement to the British Isles and has classic Laurentian geology. The key geological markers in the field used to build up a sequence of geological events are a suite of NW-SE-trending metabasic sheets – the Scourie dykes.
    [Show full text]
  • Thermobarometry of the Moine and Sgurr Beag Thrust Sheets, Northern Scotland
    Smith ScholarWorks Geosciences: Faculty Publications Geosciences 8-1-2018 Thermobarometry of the Moine and Sgurr Beag Thrust Sheets, Northern Scotland Sarah E. Mazza Virginia Polytechnic Institute and State University, [email protected] Calvin Mako Virginia Polytechnic Institute and State University Richard D. Law Virginia Polytechnic Institute and State University Mark J. Caddick Virginia Polytechnic Institute and State University Maarten Krabbendam British Geological Survey See next page for additional authors Follow this and additional works at: https://scholarworks.smith.edu/geo_facpubs Part of the Geology Commons Recommended Citation Mazza, Sarah E.; Mako, Calvin; Law, Richard D.; Caddick, Mark J.; Krabbendam, Maarten; and Cottle, John, "Thermobarometry of the Moine and Sgurr Beag Thrust Sheets, Northern Scotland" (2018). Geosciences: Faculty Publications, Smith College, Northampton, MA. https://scholarworks.smith.edu/geo_facpubs/112 This Article has been accepted for inclusion in Geosciences: Faculty Publications by an authorized administrator of Smith ScholarWorks. For more information, please contact [email protected] Authors Sarah E. Mazza, Calvin Mako, Richard D. Law, Mark J. Caddick, Maarten Krabbendam, and John Cottle This article is available at Smith ScholarWorks: https://scholarworks.smith.edu/geo_facpubs/112 Thermobarometry of the Moine and Sgurr Beag thrust sheets, northern Scotland Sarah E. Mazza1*, Calvin Mako1, Richard D. Law1, Mark J. Caddick1, Maarten Krabbendam2, John Cottle3 1Department of Geosciences, Virginia
    [Show full text]
  • A New Stratigraphic Framework for the Early Neoproterozoic Successions of Scotland
    Accepted Manuscript Journal of the Geological Society A new stratigraphic framework for the early Neoproterozoic successions of Scotland Maarten Krabbendam, Rob Strachan & Tony Prave DOI: https://doi.org/10.1144/jgs2021-054 To access the most recent version of this article, please click the DOI URL in the line above. When citing this article please include the above DOI. Received 14 May 2021 Revised 19 August 2021 Accepted 23 August 2021 © 2021 UKRI. The British Geological Survey. Published by The Geological Society of London http://creativecommons.org/licenses/by/4.0/ This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 License (http://creativecommons.org/licenses/by/4.0/) Manuscript version: Accepted Manuscript This is a PDF of an unedited manuscript that has been accepted for publication. The manuscript will undergo copyediting, typesetting and correction before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Although reasonable efforts have been made to obtain all necessary permissions from third parties to include their copyrighted content within this article, their full citation and copyright line may not be present in this Accepted Manuscript version. Before using any content from this article, please refer to the Version of Record once published for full citation and copyright details, as permissions may be required. Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/doi/10.1144/jgs2021-054/5396122/jgs2021-054.pdf by guest on 24 September 2021 A new stratigraphic framework for the early Neoproterozoic successions of Scotland Maarten Krabbendam1*, Rob Strachan2, Tony Prave3 1British Geological Survey, Lyell Centre, Research Avenue, Edinburgh EH14 4AP, Scotland, UK 2School of the Environment, Geography and Geosciences, University of Portsmouth, Portsmouth, PO1 3QL, UK.
    [Show full text]
  • Foster2018 Redacted.Pdf
    This thesis has been submitted in fulfilment of the requirements for a postgraduate degree (e.g. PhD, MPhil, DClinPsychol) at the University of Edinburgh. Please note the following terms and conditions of use: This work is protected by copyright and other intellectual property rights, which are retained by the thesis author, unless otherwise stated. A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the author. The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the author. When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given. Norse shielings in Scotland: An interdisciplinary study of setr/sætr and ærgi-names Ryan Foster Submitted for the degree of Doctor of Philosophy The University of Edinburgh 2018 Abstract This is a study of the Old Norse (hereafter abbreviated to ON) setr/sætr and ærgi place-names in areas of Scandinavian settlement in Scotland. The elements setr/sætr and ærgi all have a general meaning of a place for summer grazing in the hills, referred to in Scotland as a shieling. However, the related terms setr and sætr, are employed as shielings names in Norway and are indistinguishable from each other in Britain. It is only in areas of Scandinavian settlement in Britain and the Faroes that ærgi is found to signify a shieling site.
    [Show full text]
  • The Neoproterozoic to Mid-Devonian Evolution of Scotland: a Review and 7 Unresolved Issues
    1 1 2 3 Article-type: Article 4 5 6 The Neoproterozoic to Mid-Devonian evolution of Scotland: a review and 7 unresolved issues. 8 9 John F. Dewey1*, Ian W. D. Dalziel2, R. John Reavy3, and Rob A. Strachan4 10 11 1 University College, High Street, Oxford OX1 4BH, UK 12 2 Institute for Geophysics, Jackson School of Geosciences, The University of Texas at Austin, 13 Austin TX 78758, USA 14 3 School of Biological, Earth, and Environmental Sciences, University College Cork, Cork, 15 Ireland 16 4 School of Environmental Sciences, University of Portsmouth, Portsmouth, UK 17 18 *Correspondence ([email protected]) 19 20 r/head: Tectonic evolution of Scottish Caledonides 21 22 Abstract: The purpose of this review paper is to identify and outline some critical questions 23 about the geology and tectonic evolution of the Scottish Caledonides in their wider 24 Caledonian/Appalachian context. We outline what we think we know and what we perceive to be 25 some important problems from about 1. 0 Ga (Grenville Orogeny) to Middle Devonian (Acadian 26 Orogeny). We do not attempt in-depth analyses of any terrain or tectonic topic in this review but, 27 mainly, pose questions. Scotland is considered in the context of the Irish Caledonides and the 28 Northern Appalachians, especially Newfoundland, so we make reference to these areas where 29 appropriate. Each section is intended as “stand-alone”, not dependent upon prior or subsequent 30 sections; the sequence of sections, roughly in time order, has a historical narrative thread. We 31 have not included cross-sectional cartoons because we do not have a clear picture of plate 2 32 boundary zone and terrane arrangements in the Caledonides.
    [Show full text]
  • Timing of Regional Deformation And
    1 Timing of regional deformation and development of the Moine 2 Thrust Zone in the Scottish Caledonides: constraints from the U-Pb 3 geochronology of alkaline intrusions 4 K. M. Goodenough1, I. Millar2, R.A. Strachan3, M. Krabbendam1, and J.A. Evans2 5 1 British Geological Survey, West Mains Road, Edinburgh EH9 3LA (contact e-mail: 6 [email protected]) 7 2 NERC Isotope Geoscience Laboratory, Kingsley Dunham Centre, Keyworth, 8 Nottingham NG12 5GG 9 3 School of Earth & Environmental Sciences, University of Portsmouth, Burnaby 10 Road, Portsmouth PO1 3QL 11 12 Abstract 13 The Moine Thrust Zone in the Scottish Highlands developed during the Scandian 14 Event of the Caledonian Orogeny, and now forms the boundary between the 15 Caledonian orogenic belt and the undeformed foreland. The Scandian Event, and the 16 formation of the Moine Thrust Zone, have previously been dated by a range of 17 isotopic methods, and relatively imprecise ages on a suite of alkaline intrusions 18 localised along the thrust zone have provided the best age constraints for deformation. 19 Recent BGS mapping has improved our understanding of the structural relationships 20 of some of these intrusions, and this work is combined with new U-Pb dates in this 21 paper to provide significantly improved ages for the Moine Thrust Zone. Our work 22 shows that a single early intrusion (the Glen Dessarry Pluton) was emplaced within 23 the orogenic belt to the east of the Moine Thrust Zone at 447.9 ± 2.9 Ma. A more 24 significant pulse of magmatism centred in the Assynt area, which temporally 25 overlapped movement in the thrust zone, occurred at 430.7 ± 0.5 Ma.
    [Show full text]
  • 3 Orogenies in the Proterozoic
    Orogenies in the Proterozoic 21 3 Orogenies in the Proterozoic 3.1 Introduction Orogenies in the Proterozoic are thought to have resulted from the collision of large continental blocks and the closure of intervening oceans. These orogenic episodes are often recognized by the presence of three geological features: 1) calc-alkaline igneous rocks formed during subduction; 2) discrete suture zones containing ophiolites; and 3) remnants of high-pressure regional metamorphism that indicate periods of crustal thickening. The amalgamation of continental blocks or fragments led to the formation of large individual continental masses known as supercontinents. The periodic break-up of supercontinents led to the formation of extensive passive margins where thick sedimentary sequences accumulated. Subsequent collisions of continental fragments formed extensive linear mountain belts. Although Britain and Ireland only represent a small area of crust, the various Figure 3.1 A summary of the basement complexes and sedimentary sequences of Proterozoic age provide a geographical and time relationships of record of plate reorganizations that occurred during the time period from Late Archaean to Late Proterozoic c. 2500 Ma to c. 750 Ma. The major rock units and geological events that date rocks and events discussed in Sections from this time are summarized in Figure 3.1 and discussed in this Section, 2, 3 and 4 of this book. Moine Great Glen Thrust Fault HEBRIDEAN NORTHERN HIGHLANDS CENTRAL HIGHLANDS TERRANE TERRANE TERRANE Dalradian Supergroup SECTION 4 <806 Ma Knoydartian Orogeny c. 840–780 Ma West Highland Granitic Gneiss c . 870 Ma Dava and Sleat and Torridon Groups Moine Supergroup Glen Banchor Successions <c.
    [Show full text]
  • 349.Full.Pdf
    Neoproterozoic to early Paleozoic extensional and compressional history of East Laurentian margin sequences: The Moine Supergroup, Scottish Caledonides Peter A. Cawood1,2,†, Robin A. Strachan3, Renaud E. Merle4, Ian L. Millar5, Staci L. Loewy6, Ian W.D. Dalziel6,7, Peter D. Kinny4, Fred Jourdan4, Alexander A. Nemchin4, and James N. Connelly6,8 1Department of Earth Sciences, University of St. Andrews, Irvine Building, North Street, St. Andrews, Fife KY16 9AL, UK 2Centre for Exploration Targeting, School of Earth and Environment, The University of Western Australia, Crawley, WA 6009, Australia 3School of Earth and Environmental Sciences, University of Portsmouth, Portsmouth PO1 3QL, UK 4Department of Applied Geology, Curtin University, Perth, WA 6845, Australia 5Natural Environment Research Council Isotope Geosciences Laboratory, British Geological Survey, Keyworth, Nottingham NG12 5GG, UK 6Department of Geological Sciences, Jackson School of Geosciences, 2275 Speedway, C9000, The University of Texas at Austin, Austin, Texas 78712, USA 7Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, JJ Pickle Research Campus, 10100 Burnet Road, Austin, Texas 78758, USA 8Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5-7, Copenhagen, Denmark, DK-1350 ABSTRACT ing the breakup of Rodinia. The North At- of Laurentia (Bond et al., 1984). They consti- lantic realm occupied an external location tute a key piece of evidence that Laurentia lay Neoproterozoic siliciclastic-dominated on the margin of Laurentia, and this region at the core of the end Mesoproterozoic to early sequences are widespread along the eastern acted as a locus for accumulation of detritus Neoproterozoic supercontinent of Rodinia margin of Laurentia and are related to rift- (Moine Supergroup and equivalents) derived (Dalziel, 1991; Hoffman, 1991).
    [Show full text]
  • The Neoarchaean Uyea Gneiss Complex, Shetland: an Onshore Fragment of the Rae Craton on the European Plate
    The Neoarchaean Uyea Gneiss Complex, Shetland: an onshore fragment of the Rae Craton on the European Plate P.D. Kinny1, R.A. Strachan2, M. Fowler2, C. Clark1, S. Davis1,3, I. Jahn1,4, R.J.M. Taylor1,5, R.E. Holdsworth6 & E. Dempsey7 1. The Institute for Geoscience Research (TIGeR), School of Earth and Planetary Sciences, Curtin University, Perth, WA 6845, Australia 2. School of Earth & Environmental Sciences, University of Portsmouth, Portsmouth, PO1 3QL, UK 3. Present Address: [email protected] 4. Present address: [email protected] 5. Present Address: Department of Earth Sciences, University of Cambridge, CB2 3EQ, UK 6. Department of Earth Sciences, Durham University, Durham, DH1 3LE, UK 7. School of Environmental Sciences, University of Hull, Hull, HU6 7RX, UK Abstract: A tract of amphibolite facies granitic gneisses and metagabbros in northern Shetland, U.K., is here named the Uyea Gneiss Complex. Zircon U–Pb dating indicates emplacement of the igneous protoliths of the complex c. 2746–2726 Ma, at a later time than most of the Archaean protoliths of the Lewisian Gneiss Complex of mainland Scotland. Calc-alkaline geochemistry of the Uyea Gneiss Complex indicates arc-affinity and a strong genetic kinship among the mafic and felsic components. Zircon Hf compositions suggest an enriched mantle source and limited interaction with older crust during emplacement. Ductile fabrics developed soon after emplacement, with zircon rims at c. 2710 Ma, but there was little further deformation until Caledonian reworking east of the Uyea Shear Zone. There is no evidence for the Palaeoproterozoic reworking that dominates large tracts of the Lewisian Gneiss Complex and of the Nagssugtoqidian Orogen of East Greenland.
    [Show full text]